Elevated levels of cytochrome P4501A (CYP1A) in ringed seals from the Baltic Sea

The high frequency of a variety of disorders observed in Baltic seals have been correlated with elevated concentrations of organochlorines. For this study, we determined hepatic CYP1A activities and apoprotein levels in ringed seals ( Phoca hispida) exposed to high levels of organochlorides in the Baltic Sea and in corresponding seals from a relatively unpolluted area (Svalbard Region). Activities of ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD) in seal liver microsomes were increased about 3-fold in the Baltic sample, the EROD activity reaching similar levels to those found in 2,3,7,8-tetrachlorodibenzo- p-dioxin-induced rats (about 1,2 nmol/mg protein per min). No sex-related differences in EROD or PROD activities were observed in either population. Hepatic CYP1A levels in ringed seals were further characterised by inhibition and Western blot analysis. α-Naphthoflavone and furafylline were used as chemical inhibitors, having highly specific inhibiting effects on CYP1A1 and CYP1A2, respectively, in rat and human liver. α-Naphthoflavone inhibited potently both EROD and PROD activities, while inhibition by furafylline was weaker. A monoclonal antibody specific to CYP1A in the rat (MAb 1-7-1), used in the immunoblots, revealed a substantially increased amount of CYP1A protein in the Baltic seals. CYP2B-related proteins were not detected in any seal sample using MAb 2-66-3, which is specific for rat CYP2B. Thus, both inhibition and Western blotting experiments indicate that CYP1A is mainly responsible for the marked increase in microsomal EROD and PROD activities in the livers of Baltic ringed seals. Since the properties of all CYP enzymes vary between species, further studies are needed to verify whether CYP1A1 or CYP1A2 mediates the observed EROD induction in the ringed seal.